1. Field of the Invention
The present invention relates to an engine and a personal watercraft equipped with the engine. More particularly, the present invention relates to a dry-sump engine having a compact structure and a personal watercraft equipped with the dry-sump engine.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. In the personal watercraft, the engine is contained in a body constituted by a deck and a bull. Most of the personal watercraft are straddle-type or stand-up type personal watercraft. In either type of watercraft, the body is small and a space inside the body (hereinafter also referred to as an engine room) that contains the engine is correspondingly small.
Commonly, riders enjoy active steering on the water surface, such as rolling, yawing, pitching, or jumping over the water surface. Therefore, for oil lubrication of the engine in the personal watercraft, a dry-sump system in which an oil tank chamber is typically independent of a crankcase chamber is preferably employed. As defined herein, the dry-sump engine refers to an engine in which the oil tank chamber that reserves oil for lubricating an inside of the engine is independent of the crankcase chamber.
However, the small engine room of the personal watercraft limits design freedom in arrangement of the oil tank chamber, the crankcase chamber, and pipes for lubricating oil, when the oil tank chamber is independent of the crankcase chamber or the like and the pipes are provided between the oil tank chamber and the engine side. On the other hand, within the engine room, there exists an unused space (dead space) which is too small for the oil tank chamber independent of the crankcase chamber to be arranged therein.
In the dry-sump engine in which the oil for lubrication is fed to a cam of the cylinder head and its vicinity, it is necessary to return the oil fed to the cylinder head into the oil tank chamber. In general, the oil is dropped from the cylinder head into the crankcase chamber and then is returned into the oil tank chamber therefrom through a scavenging pump. In another method, the oil from the cylinder head is returned into an oil tank chamber independent of a crankcase chamber and then is returned into an oil tank chamber through a pump. This results in a complex structure and requires a large space. Japanese Patent No. 3004917 (corresponding to U.S. Pat. No. 5,887,564) discloses such prior art.